The present invention relates to an apparatus for the heating of plastics material pre-forms. Apparatuses of this type have long been known from the prior art. In the beverage producing industry it has become customary to produce plastic bottles, in which case plastics material pre-forms pass through a furnace, in particular an infrared furnace, for this purpose and are then shaped in this heated state in a following blow moulding machine, in particular a stretch blow moulding machine, by being acted upon with blow moulding air to form the plastics material containers. In this case furnaces of this type have to heat the respective plastics material pre-forms very exactly and to a precisely defined temperature.
In addition, it is known in this case for infrared radiators to heat the plastics material pre-forms and for the radiation to be reflected in this case by back reflectors as well as also by counter reflectors which are situated on the side of the infrared radiators arranged opposite in each case with respect to the conveying path of the plastics material pre-forms. Reflectors of this type consist in this case of ceramic material for example. It is also possible in this case for a diffuse multiple reflection to occur between these reflectors described. The long-wave portions of the infrared radiation, however, can penetrate in this case only to a poor degree into the material of the plastics material pre-forms, for example PET. This means that the surface of the plastics material pre-forms heats up more quickly than the planes of material situated at a lower level. In particular, in the case of plastics material pre-forms with a higher material strength this can lead to the surfaces thereof being excessively heated by the long-wave portions of radiation, whereas the lower-lying areas of the plastics material pre-forms are not sufficiently heated. In order therefore to be able to heat the lower-lying areas of the plastics material pre-forms sufficiently, whilst at the same time preventing the outer surface of the pre-forms from overheating and from the crystallization associated with the latter, it is known from the prior art of the Applicants to cool during the heating process.
In addition, it is known at least from the internal prior art of the Applicants for use to be made of a surface cooling of the plastics material pre-forms which will prevent the surface of the plastics material pre-forms from overheating in such a way that a so-called thermal crystallization takes place on the plastics material pre-forms. This surface cooling of the plastics material pre-forms has the drawback, however, that more air is frequently blown onto the plastics material pre-forms than is in fact required to counteract the above effect. This, however, adversely affects the energy efficiency of the furnace since it is heated and cooled at the same time.
Investigations of the Applicants have shown that highly significant energy savings can be achieved by omitting this surface cooling in the case of certain pre-forms. If, however, this cooling is dispensed with, i.e. if no air flow occurs in the furnace, the latter gradually continues to heat up. This means that on the one hand problems occur with the materials, such as for example damage as a result of excessive temperature, and on the other hand the process stability can no longer be maintained since the heating inside the furnace or respectively the internal state thereof is permanently changed.
The object of the present invention is therefore to make available an apparatus and a method of heating plastics material pre-forms, which are capable of being applied to different types of pre-forms and which nevertheless permit a uniform heating of plastics material pre-forms in every case. A further object of the invention is to increase the energy efficiency of a blow moulding machine, in particular the heating apparatus thereof. These objects are attained according to the invention by the subjects of the independent claims.